Control-Unit.md

The control unit

The control unit is a module consists of 3 eeproms controling the 24 control lines.

The micro code

The control lines

the control lines are divided to 3 8-bit eeproms.

EEPROM 0

PROGRAM COUNTER:
    PCin        | Reads the content of the bus to the PC
    PCout       | Output the content of the PC to the BUS
    PCinc       | increment the PC by 1

REGISTER FILE:
    RFin        | Reads the content of the bus to the selected register
    RFout       | Output the content of the selcted register to bus
    DSTsel      | if 1: select the dst reg, if 0: selects the src reg

INSTRUCTION REGISTER:
    IRin        | reads the content of the bus to the IR
    Vout        | output the last 4 bit of the IR to the bus

EEPROM 1

MEMORY REGISTERS:
    MARin       | reads the content of the bus to the MAR
    MDRen       | enables RD/WR to the MDR
    WRsel       | if 1: MDR is outputing data, if 0: MDR is inputing data
    MEMsel      | if 1: selects the memory, if 0: selects the bus

TIMING CONTROL:
    TCend       | reset the time control to 0
    GOTO6       | sets the time control to 6

SHIFT CONTROL:
    SCld        | reads the content of the bus to the shift cotrol
    SCdec       | decrement the shift control by 1

EEPROM 2

ALU:
    Xin         | reads the content of the bus to X-reg
    Yin         | reads the output of the ALU to Y-reg
    Yout        | output the Y-reg to the bus, also write the flags to SR
    ALUctrl[0]  | select the alu controls
    ALUctrl[1]  
    ALUctrl[2]
    ALUctrl[3]

CONDITION CONTROL:
    CONin       | input the bus to the condition logic

The input lines

CON (1bit)
SHIFT CONTROL n=0 (1bit)    
ADDRESSING MODE (2bits)
OPCODE (5bits)
TIME CONTROL (4bits)